1. Field of the Invention
This invention relates to processes for preparing anthraquinone and, in particular, to a process for preparing anthraquinone by the catalyzed vapor phase reaction of 1,3-butadiene and oxygen.
2. Description of the Prior Art
Anthraquinone, which in the pure state is a pale yellow, crystalline solid melting at 286.degree. C. and boiling at 379.degree.-381.degree. C. at atmospheric pressure, and is represented by the structural formula, ##STR1## is a valuable intermediate for the manufacture of a variety of dyes. Commercially, anthraquinone is produced by several methods, e.g., the oxidation of anthracene employing sodium dichromate and sulfuric acid; the direct catalyzed oxidation of anthracene with air or other oxygen-containing material; and, the reaction of phthalic anhydride with benzene in the presence of aluminum chloride followed by acid cyclization of the intermediate product. Still another synthesis of anthraquinone is based upon the Diels-Alder reaction of 1,3-butadiene with a mixture of naphthalene, phthalic anhydride and 1,4-naphthoquinone obtained from the vapor phase oxidation of naphthalene (viz. U.S. Pat. Nos. 1,890,040; 2,536,833; 2,652,408 and 2,938,913).